1. Field of the Invention
The invention is related to the field of an ionic probe.
2. Statement of the Problem
A measure of the ionic level of a fluid is desirable in many situations, including testing of fluids in manufacturing settings, for pharmaceutical production, food processing and/or food quality, water quality testing, etc. Measurement of an ionic level or activity can indicate completion of a reaction, indicate fractions of components, etc.
One measure can comprise a measure of a pH level, which comprises a measure of acidity of the fluid being tested. The pH measurement can indicate the acidic or basic condition or level of the fluid.
A pH measurement comprises a measurement of hydrogen ions in a solution, expressed as a logarithmic number between about zero and fourteen (sometimes extending into negative numbers for exceedingly acidic solutions). On the pH scale, a very acidic solution has a low pH value, such as zero or one, corresponding to a large concentration of hydrogen ions (H+). In contrast, a very basic solution has a high pH value, corresponding to a very small number of hydrogen ions (or to a correspondingly large number of OH− ions). A neutral solution, such as substantially pure water, has a pH value of about seven.
A pH measurement probe typically includes an active electrode unit and a reference electrode unit. The active electrode unit comprises a glass tube with an ion sensitive glass bulb at one end. The tube contains an electrolyte and an active electrode. The reference electrode unit can likewise comprise a glass tube with an ion sensitive glass bulb at one end, an electrolyte, and a reference electrode.
For each of the electrode units, the hydrated layer of glass on the exterior of the ion sensitive bulb exchanges hydrogen ions with the fluid to be tested. This produces a charge in the hydrated layer on the outside of the bulb. The internal electrolyte interacts with the ion sensitive glass and reflects a voltage potential developed in the hydrated layer of the glass due to the constant ion concentration of the electrolyte inside the glass envelope. Therefore, the voltage potential across the glass membrane is the result of the difference between the inner and outer electrical charges.
The reference buffer solution is in ionic communication with the external fluid being tested. A potential difference (i.e., voltage) between the active and reference glass electrodes is thereby formed, similar to a battery. The voltage potential between the electrodes is directly related to the ion concentration of the solution. The reference electrode provides a stable potential against which the measuring electrode can be compared. The voltage potential can be processed according to a table, formula, or other algorithm to arrive at an ionic concentration measurement, such as a pH value, for example.
The accuracy of ionic and/or pH measurements can be affected by various factors, including temperature and/or improper or contaminated electrolyte solutions, for example. A common source of inaccuracy can be an improper or inaccurate reference signal generated from a reference electrode. If the reference signal is inaccurate, the resulting pH or ion measurement will be affected. Consequently, it is of great importance that a proper and accurate reference value be obtained.